Electrical switch



NOV. 14, 1933. c, G KOPPlTi 1,935,598

ELECTRICAL SWITCH Filed May 29, 1929 Patented Nov. 14, 1933 UNITED STATES ELECTRICAL SWITCH Carl G. Koppitz, Grcensburg, Pa., assignor to Railway and Industrial Engineering Company, Greensburg, Pa., a corporation of Pennsylvania Application May 29,1929. Serial No. 367.013 17 Claims. (01. 200- 171) This invention relates to electrical switches and particularly to switches adapted to carry heavy currents.

In accordance with the present practice a large contact surface is providedrbetween the blade and the jaws of a switch and in any particular switch the contact area is determined by the current of the line in which the switch is to be placed.

Contrary to the established views, I have found that large contact areas are not necessary when the blade and jaws contact under a pressure which is exceedingly high in comparison with the area of the surfaces in contact. The jaws and blade are preferably formed of material having a high electrical conductivity and correspondingly high heat-conductive capacity. The engagement between the blade and the jaws preferably approaches a line contact such as may be attained by the engagement of a cylindrical and a plane surface, or a series of point contacts such as may be secured between spheres and a plane surface.

An object of the invention is to provide a switch in which the contact surfaces are engaged under a pressure which is exceedingly high per unit of area. A further object is to provide a switch in which the'engagement between the blade and jaws approaches line contact. More specifically an object is to provide a switch in which the current density at the contacting areas may be materially higher than in switches of the types now in use.

These and other objects of the invention will be apparent from the following description when taken with the accompanying drawing, in which Fig. 1 is a fragmentary side elevation of a knife switch;

Fig. 2 is an end elevation of the switch;

Fig. 3 is a fragmentary side elevation of a switch blade designed for effecting contact at a series of points,

Fig. 4 is a vertical section on line 4-4 of Fig. 3,

Fig. 5 is a side elevation of a modification, and

Fig. 6 is an end elevation of another type of switch construction.

In the drawing, the numeral 1 indicates the switch blade which is pivotally mounted on the support 2. The support is provided with a terminal connector 3 and with openings for receiving the bolts 4 of the insulator cap 5. The switch jaws 6 are resilient members having their lower portions integral with or fixed to the base 7 which is mounted on the insulator cap 8 and provided with a terminal connector 9.

In accordance with the invention the contact area between the blade 1 and jaws 6 is reduced to a plurality of substantially line contacts by the insertion in the end of the blade 1 of cylindrical members 10 which are of larger diameter than the width of the blade. The blade 1 and spring jaws 6 are preferably formed of copper of high electrical and thermal conductivity and the inserts 10 are preferably of a hard metal such as bronze, aluminum bronze or manganese bronze.

Accordng to the present practice the jaws of knife switches engage the blade under a pressure of or pounds. As the areas in engagement may run to several square inches, the pressure per square inch is very small. In accordance with this invention, the contact area is reduced to a magnitude of the order of an exceedingly small fraction of a square inch and the pressure per area in engagement therefore becomes exceedingly high. Although the high unit pressures undoubtedly cause some deformation of the contacting portions of the switch elements which prevents the contact from being a true line contact, the areas in contact are exceedingly small and the pressure per square inch between the blade and jaws may be of the order of 20,000 or 30,000 pounds. Unit pressures of the desired order may be obtained with spring jaws of known construction in which the jaw pressure is some 25 or 30 pounds or may be obtained with smaller jaws by increasing the pressure to, say, 80 pounds. As the current which may be safely carried by a switch of this type may be several hundred amperes and upward, the current density at the contact surfaces will be of the order of several thousand amperes per square inch. In actual practice, however, no undue heating of the jaws or blade is observed with these high current densities when the unit pressure-between the blade and jaws is of the order stated.

The use of hard metal for rubbing engagement with a softer metal prevents the wearing away of the hard metal portions and prevents scratching or cutting of the contacting parts. As the hard metal does not have a high electrical conductivity the hard metal is employed only at the contacting portion of the switch.

It will be apparent that a point or series of point contacts may be employed in place of a line contact to secure a high unit pressure, and that the plane surfaces might be provided by a knife blade of the usual construction when the cylindrical or point contacts are provided on the Jaws.

In Figs. 3 and 4, the reduced contact area is secured by providing the blade 11 with cylindrical inserts 12, the ends of the inserts being convex to effect point contact with a flat switch jaw. In the modification shown in Fig. 5, the cylindrical inserts 13 are mounted on the blades 14 which form the switch jaws, and the knife blade (not shown) then takes the form of a flat bar or strap. A corresponding arrangement of opposed. 'con- Ell) tact rods or ribs 10* on the resilient jaw members 6 is shown in Fig. 6.

It will be understood that the invention is not limited to the use of the particular unit pressures and current densities specified herein as the pressures and current densities may be adjusted to meet particular limitations as to the shape and size of the switch. The invention is characterized by the fact that the unit pressures and the current densities are materially higher than those employed in present practice, for instance pressures of a few pounds per square inch and current densities of the order of 50' to amperes per square inch.

I claim:

1. A switch comprising a hinge, a blade, and a contact member; said blade being provided with raised contact surfaces engaging the contact member with substantially point contacts when said switch is closed to eifect engagement of said blade and contact.

2. A knife switch comprising a hinge, a blade member pivoted on said hinge, and a contact member; one of said members having raised contact surfaces rigid therewith and projecting therefrom to engage the other member with substantially point contacts when said switch is closed to efiect engagement of said members.

3. A knife switch comprising a hinge member, a contact member, and a blade member pivotally supported on said hinge member for movement into engagement with said contact member, one of said members having raised and substantially rigid contact surfaces restricting the contact area between said blade member and one of the other members to an order substantially less than that of the transversely alined portions of said blade and other member.

4. In an electrical switch for carrying heavy currents, a pair of relatively movable switch members formed of relatively soft metal of high electrical and thermal conductivity, and a relatively harder metal body carried by one of said members and defining the contact area between said members.

5. In an electrical switch for carrying heavy currents, a pair of relatively movable switch members formed of soft metal of relatively high electrical and thermal conductivity, and a hard metal body carried by one of said members and engageable, upon closing of the switch, with said other member to restrict the contact area to a magnitude of the order of line contact.

6. In an electrical switch, the combination with relatively movable switch members comprising a pair of switch jaws, and a switch blade adapted to be introduced into the space between said jaws, of means for limiting the contact area of said switch to a relatively low value, said means comprising a metal insert extending through one of said switch members and projecting therefrom to define the contact area of said switch.

7. In an electrical switch for carrying heavy currents, a pair of relatively movable switch elements having the form of fiat metal bars, means for effecting movement of said elements into position parallel to and closely adjacent each other to close said switch, and a rigidly attached contact member on and projecting from the face of one of said elements, said contact member presenting a surface towards said other element which-restricts the contact area of said switch to a magnitude of the order of a l 1l f!@tion of one square inch.

8. In an electrical switch for carrying heavy currents, a switch element comprising a fiat blade formed of soft metal of relatively high electrical and thermal conductivity, and a body of relatively hard metal extending transversely through and projecting from one face of said soft metal blade.

9. An electrical switch as set forth in claim 8, wherein said body of hard metal has the form of a cylinder with convex ends.

10. In an electrical switch, a fixed contact member, a second contact member supported for movement with respect thereto, said members having fiat surfaces of substantial area presented towards each other when said switch is closed, and a contact boss on one of said members and projecting from the flat surface thereof to restrict the contacting area of said elements to an order not exceeding that of line contact.

11. The invention as set forth in claim 10, wherein said, members are formed of relatively soft metal of high electrical and thermal conductivity, and said contact boss is metal of greater hardness and lower electrical and heat conductivity.

12. The invention as set forth in claim 10, wherein said boss consists of a cylinder of hard metal secured in and completely filling an aperture in the member which carries said boss.

13. An electrical switch adapted to carry heavy currents, and of the type including a pair of relatively movable switch elements having the form of fiat metal bars, and contact surfaces projecting beyond the body of one of said elements to engage the other element, thereby to restrict the 3110 contact area of said elements to a magnitude of the order of less than surface contact, characterized by the fact that said elements are formed of soft metal of relatively high electrical and thermal conductivity, and the projecting con- 1115 tact surfaces are of harder metal having lower electrical and thermal conductivity than said elements.

14. In a switch, a jaw comprising a pair of substantially parallel plates anchored at their 121i lower ends, having outwardly curved upper ends for guiding a knife blade between the plates, and provided intermediate their ends with opposed inwardly extending and substantially rigid ribs to form lines contact with the blade. E25

15. In a switch, a jaw contact element comprising a pair of substantially parallel plates anchored at their lower ends and having outwardly curved upper ends, and a blade contact element adapted to be guided between said plates 1% by the curved upper ends of said jaw contact element, one of said contact elements being provided with opposed and substantially rigid ribs to form line contacts with the other contact element.

16. In a switch, a jaw comprising a pair of substantially parallel plates provided with outwardly curved end portions for guiding a knife blade between said plates and provided adjacent said curved end portions with rigid means to form line contact with the blade.

17. In a switch, a jaw comprising a pair of substantially parallel plates provided with outwardly curved end portions for guiding a knife blade between said plates and provided adjacent said curved end portions with opposed co-acting inwardly projecting transversely extending embossed portions to form line contact with the blad CARL G. KOPPITZ. 

